The high levels of productivity achieved in modern agriculture have been largely the result of quite recent knowledge gained on effective means of applying sprays of fertilizers and herbicides. No-till farming is a new area in which soil is preserved and fertilizer requirements lowered by killing residual plants with a topical herbicide and using a seed drill to insert seed and spray nozzles to apply liquid fertilizer. But even this method of farming is limited by the requirement for separate applications of herbicide and fertilizer due to the incompatibility of the herbicide with the fertilizer suspending agent. As a result, two passes are required over the field instead of one which would be possible if a new suspending agent were available, which was not incompatible with the herbicide. U.S. Pat. No. 4,874,854 discloses comparative examples of polymers which are incompatible with the herbicide Paraquat.RTM..
U.S. Pat. Nos. 3,526,495, 3,679,390 and 4,315,763 teach that a wide variety of calcium salts cause gelling and thickening of fertilizers, similar to iron salts as described in U.S. Pat. Nos. 4,056,381 and 4,336,053. The first three references teach the equivalency of calcium chloride with other calcium salts, while a combination of all five references would suggest to a person of ordinary skill in the art that both calcium and iron salts can perform the same functions as fertilizer suspending agents. U.S. Pat. No. 4,118,218 discloses a process for preparing granular herbicidal compositions using an inert sodium or calcium chloride carrier.
U.S. Pat. No. 3,526,495 and U.S. Pat. No. 3,679,390 further illustrate that the present invention represents a long sought after result on which considerable time and effort has been expended. Whereas all prior art practitioners had the same goals and all materials were readily available, their disclosures all teach away from the discovery contained herein.
When clay is used as a suspending agent for fertilizer, the suspension produced has limited stability and tends to settle in about 24 hours. Thus, when trucks are not able to go into fields to spray the liquid fertilizer because of rain, it is necessary to unload the trucks and remix the liquid fertilizer. Therefore, it would be an advance in the state-of-the-art to have a liquid fertilizer composition which would not settle even if weather or mechanical delays put off field application.
A separate problem with clay suspensions is that they are difficult to prepare. While clay is a readily available and low cost material, preparation of the clay suspension is both time consuming and labor intensive. Thus it would be a further advance to be able to use a low cost and readily available suspension agent which could avoid the shortcomings of clay.
Clay is known to be a useful absorbent. However, this property would be detrimental if clay removed effective amounts of herbicide from a suspension. Thus a new type of suspension in which both fertilizer and herbicide could be applied from one composition would be a monumental advance for agriculture.
A further disadvantage of prior art clay suspensions of liquid fertilizers is the inability to incorporate desirable quantities of potash (potassium chloride) without encountering precipitation problems. As a practical limit it is difficult to prepare a clay suspension containing more than 10% by weight potash. Thus, the availability of a suspending agent which would allow incorporation of more than 10% by weight potash in the liquid fertilizer would be a significant advance. It would not have been apparent to employ calcium chloride for such a purpose in view of literature reports that precipitation rather than suspension would occur.
It is known that individual calcium salts are capable of performing unique functions; wherein other calcium salts are ineffective. U.S. Pat. No. 4,859,208 discloses and claims calcium citrate in a print paste composition.